A. Technical Field
The present invention relates to a purification process for hydroxyalkyl (meth)acrylate.
B. Background Art
Hydroxyalkyl (meth)acrylate is generally obtained by reacting (meth)acrylic acid and alkylene oxide in the presence of a catalyst. However, hydroxyalkyl (meth)acrylate is formed as an objective product and at the same time by-products such as alkylene glycol di(meth)acrylate (hereinafter donated to xe2x80x9cdiesterxe2x80x9d), dialkylene glycol (meth)acrylate and a dimer of acrylic acid are formed in this production process. Accordingly, a purification process is necessary.
As a general purification process up to this day, a process comprising the step of distilling a reaction solution in a reduced pressure in order to separate and purify is carried out (JP-B-300/1982). However, in this process, for example, in case where a distillation column was used, hydroxyalkyl (meth)acrylate coexistent with a catalyst used for the reaction for a long time was exposed to a comparatively high temperature. Therefore, the diester and the dimer of acrylic acid produced from remaining acrylic acid were increased, a purity of hydroxyalkyl (meth)acrylate as an objective product lowered and a problem as to a production quality rose because disproportionation reaction of this hydroxyalkyl (meth)acrylate was apt to occur. In addition, there is another problem that polymerization of hydroxyalkyl (meth)acrylate is apt to occur in staying at a high temperature because hydroxyalkyl (meth)acrylate has a very high polymerizability.
On the other hand, a process utilizing a thin-film evaporation apparatus (which might be called thin-film evaporator) was considered (German Patent No. 152540) in order to avoid long staying at a high temperature. However, this process was excellent in suppression of by-products and inhibition of polymerization, and the thin film of evaporating surface was maintained by rotating a cylindrical object and paddling a solution on the evaporating surface with a wiper in the thin-film evaporation apparatus. However, there were problems that a splash and an entrainment easily produced by rotating and paddling in order to form a liquid film and a distilled product is easily contaminated with the splash and the entrainment.
A. Object of the Invention
An object of the present invention is to provide: a purification process for hydroxyalkyl (meth)acrylate that suppresses forming by-products such as a diester and a dimer of acrylic acid in the distillation process, and can ensure a purity of hydroxyalkyl (meth)acrylate, and can operate stably without causing troubles such as polymerization.
B. Disclosure of the Invention
The present inventors diligently studied to solve the above-mentioned problems. As a result, they hit on an idea that: in a purification process for hydroxyalkyl (meth)acrylate, which comprises the steps of obtaining a reaction solution by reacting (meth)acrylic acid and alkylene oxide in the presence of a catalyst, removing unreacted alkylene oxide and/or (meth)acrylic acid in the reaction solution, and thus obtaining the hydroxyalkyl (meth)acrylate, a mode that a distillation apparatus having a portion of a vacant column and a thin-film evaporation apparatus are used at the same time is adopted, thereby purification of hydroxyalkyl (meth)acrylate can be carried out without causing prior problems owing to a multiplicated effect derived from characteristics that these apparatuses have respectively and using these apparatuses at the same time. Concretely, they found that: a residence time for a solution at a high temperature can be shortened in the presence of the catalyst by using the thin-film evaporation apparatus at the same time, impurities can be suppressed to form, and a purity of a product can be ensured if the problem of contaminating with the splash and the entrainment is caused not to arise by returning the treated product to the distillation apparatus. The present invention was completed in this way.
That is to say, a purification process for hydroxyalkyl (meth)acrylate, according to the present invention, comprises the steps of: obtaining a reaction solution by reacting (meth)acrylic acid and alkylene oxide in the presence of a catalyst, removing unreacted alkylene oxide and/or (meth)acrylic acid in the reaction solution, and thus obtaining the hydroxyalkyl (meth)acrylate,
and this purification process is characterized in that a distillation apparatus having a portion of a vacant column and a thin-film evaporation apparatus are used at the same time.
These and other objects and the advantages of the present invention will be more fully apparent from the following detailed disclosure.